The present invention relates to a method and apparatus for the manufacture of thin film magnetic transducers and, more particularly, to a lapping process which minimizes inter-element shorting at the air bearing surface of a magnetoresistive read transducer.
In high speed data processing systems, magnetic recording has been employed for large memory capacity requirements. In magnetic disk drive systems, data is read from and written to magnetic recording media utilizing magnetic transducers commonly referred to as magnetic heads. Typically, one or more magnetic recording disks are mounted on a spindle such that the disks can rotate to permit the magnetic head mounted on a moveable arm in position closely adjacent to the disk surface to read or write information thereon.
During operation of the disk drive system an actuator mechanism moves the magnetic transducer to a desired radial position on the surface of the rotating disk where the head electromagnetically reads or writes data. Usually, the head is integrally mounted in a carrier or support referred to as a "slider". A slider generally serves to mechanically support the head and any electrical connections between the head and the rest of the disk drive system. The slider is aerodynamically shaped to glide over moving air and therefore to maintain a uniform distance from the surface of the rotating disk thereby preventing the head from undesirably contacting the disk.
Typically, a slider is formed with two parallel rails having a recessed area between the rails and with each rail having a ramp at one end. The surface of each rail that glides over the disk surface during operation is known as the air bearing surface.
A head is typically an inductive electromagnetic device including magnetic pole pieces which read the data from or write the data onto the recording media surface. Alternatively, the magnetic head may include a magnetoresistive read element for separately reading the recorded data with the inductive head serving to only write the data. In either case, the inductive head magnetic pole pieces and MR head elements terminate on the air bearing surface and function to electromagnetically interact with the data contained in the magnetic recording disk.
In manufacturing such read/write heads, a large number of sliders are fabricated from a single wafer having rows of the magnetic transducers deposited simultaneously on the wafer surface using semiconductor-type process methods. After deposition of the heads is complete, single-row bars are sliced from the wafer, each bar comprising a row of units which can be further processed into sliders having one or more magnetic transducers on their end faces. Each row bar is bonded to a fixture or tool where the bar is processed and then further diced, i.e., separated, into individual sliders, each slider having at least one magnetic head terminating at the slider air bearing surface.
In order to achieve maximum efficiency from the magnetic heads, the sensing elements must have a pole tip height dimension, commonly referred to as throat height for the thin film inductive heads, or element height in the case of MR read heads, which must be maintained within a certain limited tolerance for generating a maximum signal from a given head element. During the row bar processing, it is critical to grind or lap the bar to a desired thickness in order to achieve the desired throat height and MR element height.
Prior art conventional lapping processes utilize either oscillatory or rotary motion of the work piece (i.e., the row bar) across either a rotating or oscillating lapping plate to provide a random motion of the work piece over the lapping plate and randomize plate imperfections across the head surface in the course of lapping. For example, see U.S. Pat. No. 4,536,992 granted to Hennenfent on Aug. 27, 1985 wherein a work piece is supported by the free end of a pivotly mounted arm on the surface of a rotating lapping plate. During the lapping process, the motion of abrasive grit carried on the surface of the lapping plate is typically transverse to or across the magnetic head elements exposed at the slider air bearing surface. In magnetic heads, particularly MR heads, the electrically active components exposed at the air bearing surface are made of relatively soft or ductile materials. During the lapping process, these electrically active components can scratch and smear into other components causing electrical shorts and degraded head performance. With high density recording MR heads, the smearing becomes severe enough to result in substantial manufacturing yield loss.
The prior art lapping process also causes different materials exposed at the slider air bearing surface to lap to different depths resulting in recession of the critical head elements relative to the air bearing surface and thus poor head performance because of increased spacing between the critical elements and the recording disk. This recession is further aggravated by the random motion of the lapping plate surface across the exposed head elements.